Reciprocating pump systems, such as sucker rod pump systems, extract fluids from a well and employ a downhole pump connected to a driving source at the surface. A rod string connects the surface driving force to the downhole pump in the well. When operated, the driving source cyclically raises and lowers the downhole pump, and with each stroke, the downhole pump lifts well fluids toward the surface.
For example, FIG. 1 shows a sucker rod pump system 10 used to produce fluid from a well. A downhole pump 14 has a barrel 16 with a standing valve 24 located at the bottom. The standing valve 24 allows fluid to enter from the wellbore, but does not allow the fluid to leave. Inside the pump barrel 16, a plunger 20 has a traveling valve 22 located at the top. The traveling valve 22 allows fluid to move from below the plunger 20 to the production tubing 18 above, but does not allow fluid to return from the tubing 18 to the pump barrel 16 below the plunger 20. A driving source (e.g., a pump jack or pumping unit 11) at the surface connects by a rod string 12 to the plunger 20 and moves the plunger 20 up and down cyclically in upstrokes and downstrokes.
During the upstroke, the traveling valve 22 is closed, and any fluid above the plunger 20 in the production tubing 18 is lifted towards the surface. Meanwhile, the standing valve 24 opens and allows fluid to enter the pump barrel 16 from the wellbore.
At the top of stroke, the standing valve 24 closes and holds in the fluid that has entered the pump barrel 16. Furthermore, throughout the upstroke, the weight of the fluid in the production tubing 18 is supported by the traveling valve 22 in the plunger 20 and, therefore, also by the rod string 12, which causes the rod string 12 to stretch. During the downstroke, the traveling valve opens, which results in a rapid decrease in the load on the rod string 12. The movement of the plunger 20 from a transfer point to the bottom of stroke is known as the “fluid stroke” and is a measure of the amount of fluid lifted by the pump 14 on each stroke.
Because there are no sensors to measure conditions at the downhole pump 14, which may be located thousands of feet underground, surface measurements of the position and load for the rod string 12 at the pump jack 11 are used with numerical methods to calculate the position of the pump plunger 20 and the load acting on the plunger 20. These surface measurements are typically made at the top of the polished rod 15, which is a portion of the rod string 12 passing through a stuffing box 13 at the wellhead. A pump controller 26 is used for monitoring and controlling the pump system 10.
To efficiently control the reciprocating pump system 10 and avoid costly maintenance, the rod pump controller 26 can gather system data and adjust operating parameters of the system 10 accordingly. Typically, the rod pump controller 26 gathers system data such as load and rod string displacement by measuring these properties at the surface.
Current pumping units, such as the pump jack 11, are counterbalanced to reduce the energy consumption. The counterbalance subsystem uses weights 36 attached at predetermined points along crank arms 34 to offset a portion of the rod load in the well. The position of these weights 36 is normally calculated as a part of the initial setup and is based upon numerous factors including, but not limited to, the physical characteristics (length, weight, etc.) of the rod string 12, the fluid load, the size of the pumping unit 11, the type of gearbox 32, the type of motor 30, etc. The calculations involved in setting up the weight's position have been known for many years by those skilled in the art of conventional pumping units.
During the course of normal pumping operations, however, the rod loads may change. This results in a condition known as “out-of-balance,” and it is desirable to correct this condition. Otherwise, the energy usage increases, and the operation of the pumping unit 10 is not optimal, which can reduce the operating life of some of the components.
For many years, operators have inserted an electrical meter, such as an ammeter or tachometer, across terminals of the motor 30 of the unit 100 as a means of determining the severity of the “out-of-balance” condition. For example, the ammeter can directly measure the peak current on the upstroke and the downstroke. Once the measurement is taken, a calculation is made to determine what the new placement of the counterbalance weights 36 should be. However, in most cases, installing the ammeter or tachometer requires a high voltage electrical cabinet to be opened so leads of the meter can be attached to the motor terminals. This is not a desired practice.
The subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.